U.S. patent application number 10/513760 was filed with the patent office on 2005-10-13 for device and method for measuring axial force of bolt.
Invention is credited to Nakamura, Takanori.
Application Number | 20050223804 10/513760 |
Document ID | / |
Family ID | 31184586 |
Filed Date | 2005-10-13 |
United States Patent
Application |
20050223804 |
Kind Code |
A1 |
Nakamura, Takanori |
October 13, 2005 |
Device and method for measuring axial force of bolt
Abstract
The present invention provides an axial bolt force measuring
instrument for measuring an axial force of a bolt for a hub that
couples a wheel and an axle of a vehicle, where the instrument is
provided with a setting portion that sets a predetermined axial
force of the bolt, a tapping portion that taps the bolt, a sound
collecting portion that collects tap sound generated by tapping the
bolt with the tapping portion, a frequency measuring portion that
measures a frequency of the tap sound collected by the sound
collecting portion, an axial force converting portion that converts
the frequency of the tap sound measured by the frequency measuring
portion into an axial force of the bolt, a comparing portion that
compares the set axial force set in the setting portion with the
converted axial force converted in the axial force converting
portion from the frequency of the tap sound, and a display portion
that displays a result of comparison in the comparing portion.
Inventors: |
Nakamura, Takanori;
(Niigata-shi, JP) |
Correspondence
Address: |
HAUPTMAN KANESAKA BERNER PATENT AGENTS
SUITE 300, 1700 DIAGONAL RD
ALEXANDRIA
VA
22314-2848
US
|
Family ID: |
31184586 |
Appl. No.: |
10/513760 |
Filed: |
November 9, 2004 |
PCT Filed: |
July 9, 2003 |
PCT NO: |
PCT/JP03/08707 |
Current U.S.
Class: |
73/581 |
Current CPC
Class: |
G01N 2291/02827
20130101; G01L 5/246 20130101 |
Class at
Publication: |
073/581 |
International
Class: |
G01L 005/00; G01L
001/10 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 25, 2002 |
JP |
2002-216773 |
Claims
1. An axial bolt force measuring instrument for measuring an axial
force of a bolt for a hub that couples a wheel and an axle of a
vehicle, the instrument comprising: a setting portion that sets a
predetermined axial force of the bolt; an initiation operation
portion that is operated to start measurement; a tapping portion
which is brought into contact with the bolt, and is operated by
initiation operation from the initiation operation portion to tap
the bolt continuously a plurality of times in a predetermined
stroke; a sound collecting portion which is brought into contact
with the bolt, and collects tap sound generated by the tapping
portion tapping the bolt; a frequency measuring portion that
measures a frequency of the tap sound collected by the sound
collecting portion; an axial force converting portion that converts
the frequency of the tap sound measured by the frequency measuring
portion into an axial force of the bolt; a comparing portion that
compares a set axial force set in the setting portion with a
converted axial force converted in the axial force converting
portion from the frequency of the tap sound; and a display portion
that displays a result of comparison in the comparing portion,
wherein the instrument is a one-piece instrument.
2. The axial bolt force measuring instrument according to claim 1,
wherein the tapping portion has an impact chip that comes into
contact with the bolt, and hardness of the impact chip is greater
than hardness of the bolt subject to measurement.
3. The axial bolt force measuring instrument according to claim 1,
wherein the display portion displays the axial force of the bolt
converted in the axial force converting portion.
4. The axial bolt force measuring instrument according to claim 1,
wherein the axial force converting portion converts the frequency
of the tap sound into the axial force of the bolt corresponding to
a size of the bolt.
5. The axial bolt force measuring instrument according to claim 4,
wherein the axial force converting portion converts the frequency
of the tap sound into the axial force of the bolt corresponding to
a material of the bolt and a material of a member fastened by the
bolt.
6. The axial bolt force measuring instrument according to claim 1,
wherein the instrument is formed of: an instrument body internally
provided with the tapping portion, the sound collecting portion,
the frequency measuring portion, and the axial force converting
portion; and a handle portion which enables grasp thereof by hand,
extends from the instrument body, and has an initiation portion
that initiates the tapping portion.
7. The axial bolt force measuring instrument according to claim 6,
further comprising: an internal battery that supplies power
required for measurement of the axial force of the bolt.
Description
TECHNICAL FIELD
[0001] The present invention relates to an axial bolt force
measuring instrument and method for measuring an axial force
(tightening force) of a bolt, and more particularly, to an axial
bolt force measuring instrument for measuring an axial force
(tightening force) of a bolt for a hub that couples a wheel and an
axle of a vehicle i.e. a hub bolt that fastens the wheel to the
hub.
BACKGROUND ART
[0002] Generally, a wheel of a vehicle is coupled to an axle
through a hub. In this case, the wheel and hub are fastened by a
bolt (hereinafter referred to as a hub bolt) and nut. When the nut
is fixed and the hub bolt is rotated in the fastening direction,
the wheel and hub are compressed, while a tension (axial force or
tightening force) is applied to the hub bolt, and the hub bolt
extends. In the assembling operation or the like, it is important
to adequately control the tightening fore (axial force) of the hub
bolt to maintain at a proper value. This is because of a risk that
the hub and/or wheel is deformed or broken, when the fastening is
not adequate and/or tightening is excessively applied.
[0003] Various methods have conventionally been known, as a method
for controlling the tightening force (axial force) of a hub bolt.
For example, methods have been well known that a tightening torque
is set at a predetermined value using a torque wrench, or a skilled
mechanic or the like taps each portion of a bolt fastening member
using a micro hammer, and based on the tap sound, inspects a
tightening state of the hub bolt. Further, an ultrasonic applying
measurement tester has also been known which applies ultrasonic
pulses to a tightened hub bolt from an end surface in the axial
direction, obtains a length (elongation) of the hub bolt from the
time required for the reflective wave to return, and using the bolt
length, calculates the axial force of the hub bolt.
[0004] However, in the method of using the torque wrench, the use
is predicated on the muscular strength of a person, and therefore,
limited to small-size vehicles or the like. In this torque wrench
method, since the tightening torque is set at a predetermined value
and the bolt is merely tightened to the set value, it is not
possible to examine and/or measure the axial force itself of the
hub bolt after the bolt is tightened. Further, in the torque wrench
method, an unstable factor of torque coefficients is considered as
a defect.
[0005] Meanwhile, in the inspection method using the tap sound with
a micro hammer, since decision is made by listening based on the
skill and intuition without the rating, it is not possible to
examine and/or measure a fastening state of the hub bolt with
accuracy.
[0006] Further, in the method using the ultrasonic applying
measurement tester, since the axial force of the hub bolt is
obtained by calculating an elongation of the hub bolt targeted for
the test using correlation, it is required to perform measurement
at least twice, prior to and subsequent to bolt fastening, to
determine the elongation of the hub bolt. Accordingly, there are
limitations in time required for measurement and reduction in cost.
Furthermore, the conventional ultrasonic applying measurement
tester has a separate sensor portion and amplifier portion and thus
a plurality of components, thereby is not suitable for operation
requiring portability, nor does not have a power source, and
therefore, can be used only in places with a commercial power
source.
DISCLOSURE OF INVENTION
[0007] It is an object of the present invention to provide an axial
bolt force measuring instrument with excellent portability and
general versatility enabling the axial force (fastening state) of a
tightened bolt to be measured promptly and accurately.
[0008] Therefore, the present invention provides an axial bolt
force measuring instrument which measures an axial force of a bolt
for a hub that couples a wheel and an axle of a vehicle, and which
is integrally provided with a setting portion that sets a
predetermined axial force of the bolt, an initiation operation
portion that is operated to start measurement, a tapping portion
which is brought into contact with the bolt, and is operated by
initiation operation from the initiation operation portion to tap
the bolt continuously a plurality of times in a predetermined
stroke, a sound collecting portion which is brought into contact
with the bolt and collects tap sound generated by the tapping
portion tapping the bolt, a frequency measuring portion that
measures a frequency of the tap sound collected by the sound
collecting portion, an axial force converting portion that converts
the frequency of the tap sound measured by the frequency measuring
portion into an axial force of the bolt, a comparing portion that
compares a set axial force set in the setting portion with a
converted axial force converted in the axial force converting
portion from the frequency of the tap sound, and a display portion
that displays a result of comparison in the comparing portion.
BRIEF DESCRIPTION OF DRAWINGS
[0009] FIG. 1 is a conceptual view of a primary portion enlarged
section of an axial bolt force measuring instrument according to
the present invention;
[0010] FIG. 2 is a schematic block diagram of the axial bolt force
measuring instrument according to the present invention;
[0011] FIG. 3 is a side view of an axial bolt force measuring
instrument according to one embodiment of the present
invention;
[0012] FIG. 4 is a graph showing the correlation between the axial
bolt force and the frequency of tap sound;
[0013] FIG. 5 is a schematic internal configuration view of the
axial bolt force measuring instrument according to one embodiment
of the present invention; and
[0014] FIG. 6 is a flowchart showing measuring procedures of the
axial bolt force measuring instrument according to one embodiment
of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0015] A preferred embodiment of the present invention will
specifically be described below with reference to accompanying
drawings.
[0016] FIGS. 1 and 2 conceptually show an axial bolt force
measuring instrument according to the present invention. As can be
seen from the figures, the axial bolt force measuring instrument
according to the present invention taps a hub bolt, and measures an
axial force of the bolt from the frequency of the tap sound. First,
the principle will be described below.
[0017] Generally, when a tension is generated on an object and the
object is hit, unique sound is generated. The frequency of the hit
sound varies with level of the tension of the hit object
(representative examples of application of this principle are
musical instruments, and tuning of a piano, guitar or the like is
performed by increasing/decreasing the tension of chords). For
example, when a rigid body under a tension is hit by an object with
a higher degree of hardness than that of the rigid body, the
frequency of the hit sound caused by hitting has the correlation
with the tension of the rigid body, and increases as the tension is
higher, while decreasing as the tension is lower. In practical
phenomenon, for example, the sound with a high frequency occurs
generally in a normal fastening portion (when normal tension occurs
on a rigid body) in a metal component subjected to heat processing,
while the dull sound with a low frequency occurs in portions with
corrosion, breakage, distortion, crack, etc.
[0018] It is a basic concept of the present invention to apply the
aforementioned principle to measurement of an axial bolt force. In
other words, fastening a bolt and nut is the operation for
generating a tension on the bolt, and whether or not the bolt is
tightened by a predetermined tightening torque (axial force) can be
determined by measuring whether or not a predetermined tension is
generated on the bolt. Further, the tension is measured from the
frequency of the hit sound by hitting the bolt.
[0019] Based on such a principal, as shown in FIGS. 1 and 2, an
axial bolt force measuring instrument 1 according to the present
invention is provided with an initiation operation portion 2 to be
operated to start measurement, a main circuit 4 that receives an
initiation signal from the initiation operation portion 2, a
tapping device 6 which is brought into contact with a bolt 14
subject to measurement and based on a control signal from the main
circuit 4 due to the initiation signal, operates and hits the bolt
14, a sound collecting microphone 8 that collects hit sound (tap
sound) from the bolt 14 by the tapping device 6, a setting device
12 to set and input a proper axial force (predetermined value) of
the bolt subject to measurement, for example, at a predetermined
range, and a display device 10 that displays a result of
measurement.
[0020] In this configuration, the frequency of the hit sound
collected by the sound collecting microphone 8 is measured, and the
measured value is compared with a reference value in the main
circuit 4. More specifically, the main circuit 4 has a storage
portion that stores correlation data (that is beforehand determined
by experiments or the like) between the frequency and the axial
bolt force (tension), obtains an axial bolt force corresponding to
the frequency measured value from the correlation data stored in
the storage portion, and determines whether or not the axial bolt
force agrees with a proper value (reference value) set and input by
the setting device 12 (whether or not the axial bolt force
converted from the frequency is in a range of proper values set and
input by the setting device 12, when a predetermined range is set
and input as the proper axial force) by comparison. Then, the
result of determination is displayed on the display device 10. In
addition, in FIG. 1, "16" denotes a nut combined with the bolt 14,
and "18" denotes a member fastened by the bolt 14 and nut 16.
[0021] As described above, the axial bolt force measuring
instrument 1 according to the present invention causes the tapping
device 6 to hit the bolt 14, measures the frequency of the hit
sound generated by hitting, compares the measured value with a
reference value (a single value (or a range of values) set and
input by the setting device), and thus functions as a tester that
inspects and diagnoses the level of the axial force (tension) of
the bolt 14. As is understood from the foregoing, the basic use
mode of the axial bolt force measuring instrument according to the
present invention is similar to that of the previously-mentioned
conventional method for lightly hitting each portion of the
construction using a micro hammer to inspect. However, the method
using the axial bolt force measuring instrument according to the
present invention is to accurately measure the axial force of the
bolt by detecting the tap sound electrically to process, and in
this respect, has the most significant difference from the
conventional inspection method using a micro hammer which makes a
decision by listening based on the skill and intuition without the
rating.
[0022] An embodiment of the present invention based on the
aforementioned principal will be described specifically below with
reference to FIGS. 3 to 6.
[0023] As shown in FIGS. 3 to 5, an axial bolt force measuring
instrument 1A of this embodiment has a substantially gun-shaped
form, and comprised of a gun-barrel-shaped main body portion
(measuring instrument body) 42 and a handle portion 40 enabling
grasp thereof by hand. The handle portion 40 is provided with a
trigger lever 2A as an initiation operation portion capable of
being operated by a finger of the hand grasping the handle portion
40 to start measurement. The trigger lever 2A is electrically
connected to a driving control portion 22 of a main substrate (main
circuit) 4A described later. Further, inside the handle portion 40
is provided a battery 20 that supplies power to each electrical
component (described later) including the main substrate 4A.
[0024] The main body portion 42 is provided with a setting portion
12A in which, for example, a predetermined range is set and input
as a proper axial force (reference value; predetermined value) of
the bolt subject to measurement, and a display portion 10A that
displays a result of measurement. The display portion 10A has a
display panel 10a exposed on the side wall of the main body portion
42 as shown in FIG. 3. The display panel 10a is provided with a
plurality of LEDs (display means) capable of displaying a result of
measurement (determination) of whether or not the measured axial
force of the bolt is a proper axial force, for example, in a
plurality of modes, and a display that displays a measured value of
the axial bolt force. Meanwhile, the setting portion 12A also has a
setting panel 12a exposed on the side wall of the main body portion
42 as shown in FIG. 3. The setting panel 12a is provided with at
least various kinds of setting buttons to set the size of the bolt
to measure and others pertinent to the correlation data described
later, and a display that displays values set by the setting
buttons. In addition, the display portion 10A and setting portion
12A are electrically connected to a comparison computing
determination circuit 24, described later, of the main substrate
4A.
[0025] On the front end surface of the main body portion 42 is
provided an impact chip 6A as a tapping device (tapping portion)
that comes into contact with the bolt subject to measurement and
that continuously hits the bolt. The hardness of the impact chip 6A
is set higher than the hardness of the bolt subject to
measurement.
[0026] The impact chip 6A is attached to the tip of a plunger
solenoid 32 that is electrically connected to the driving control
portion 22 of the main substrate 4A, and continuously hits the bolt
by a traveling driving portion of the plunger solenoid 32 traveling
back and forth in a stroke of about 5 mm using a control signal
from the driving control portion 22 (for example, the chip 6A
operates for about two seconds at speed of tapping three times a
second).
[0027] Further, on the front end surface of the main body portion
42 is provided a sound collecting microphone (sound collecting
portion) 8A that collects hit sound (tap sound) generated by
tapping the bolt by the impact chip 6A. The sound collecting
microphone 8A is electrically connected to the comparison computing
determination circuit 24 of the main substrate 4A via an amplifier
26 and an A/D frequency conversion circuit (frequency measuring
portion) 28. In this case, the amplifier 26 amplifies a sound
signal due to the hit sound collected by the sound collecting
microphone 8A. The A/D frequency conversion circuit 28 converts the
sound signal as an analog signal amplified by the amplifier 26 into
a digital signal to output to comparison computing determination
circuit 24.
[0028] Furthermore, on the front end surface of the main body
portion 42 is provided an inkjet nozzle 34 capable of providing the
bolt with marking, for example, of a result of measurement. The
inkjet nozzle 36 is connected to a plunger solenoid valve 30 that
is electrically connected to the driving control portion 22 of the
main substrate 4A, and sprays ink from an ink tank 36 to the bolt
by the operation of the plunger solenoid valve 30.
[0029] The main substrate 4A is provided with the driving control
portion 22 and the comparison computing determination circuit
(comparing portion; axial force converting portion) 24. The driving
control portion 22 generates a control signal to drive the plunger
solenoid 32 of the impact chip 6A in response to a trigger signal
due to the operation of the trigger lever 2A, and further generates
a control signal to drive the plunger solenoid valve 30 of the ink
jet nozzle 34 in response to a determination signal from the
comparison computing determination circuit 24.
[0030] Meanwhile, the comparison computing determination circuit 24
receives a digital signal with the frequency corresponding to the
hit sound collected by the sound collecting microphone 8A from the
A/D frequency conversion circuit 28, converts (computes) the
frequency data of the digital signal into an axial bolt force,
while comparing the converted value with a set value (predetermined
proper axial bolt force) set and input in the setting portion 12A,
and determines whether or not the axial bolt force is proper.
[0031] More specifically, the comparison computing determination
circuit 24 stores the correlation data (that is beforehand obtained
from experiments or the like) between the tap sound frequency (the
frequency of hit sound by tapping the bolt by the impact chip 6A)
and the axial bolt force, obtains an axial bolt force corresponding
to the measured frequency value (of the digital signal received
from the A/D frequency conversion circuit 28) from the stored
correlation data, and determines whether or not the axial bolt
force agrees with the set value set and input in the setting
portion 12A (whether or not the axial bolt force converted from the
frequency measured value is in a range of the proper value set and
input in the setting portion 12A, when a predetermined range is set
and input as the proper axial force) by comparing the values. The
correlation data between the frequency and axial bolt force is
stored for each size of the bolt and for each material of the bolt
and a member related to bolt fastening. When the size, material and
others of the bolt to measure are set in the setting portion 12A,
the comparison computing determination circuit 24 converts the
frequency measured value into the axial bolt force using the
correlation data corresponding to the set value.
[0032] In addition, a parameter other than the size of the bolt and
materials may be adopted for the correlation data. As an example of
the correlation data, FIG. 4 shows the correlation data between the
tap sound frequency and the axial bolt force of an M20 bolt
(surface hardness 454 HV) with a strength class of 12.9 that is a
central class of 1.8T series in JIS B1051 Table 1-7.
[0033] With reference to a flowchart in FIG. 6, a case will be
described below of measuring an axial force of a bolt for a hub
that couples a wheel and an axle of a vehicle i.e. a hub bolt to
fasten the wheel to the hub.
[0034] In addition, in this case, the hub corresponds to the member
18 in FIG. 1, the hub nut corresponds to the nut 16 in FIG. 1, and
the hub bolt corresponds to the bolt 14 in FIG. 1. In the case of
measuring the axial bolt force of a middle-size vehicle using hub
bolts with a nominal bolt diameter of 18 mm to 20 mm
(M18.about.M22), for example, when the surface hardness of the hub
bolt with the nominal diameter of 20 mm (M20) is 454 HV in JIS, the
surface hardness of the impact chip 6A is set at 520 HV harder than
454 HV. Further, it is assumed that the comparison computing
determination circuit 24 stores the correlation data between the
tap sound frequency and the axial bolt force in a no-load state
where any load is not mounted on the vehicle for each size of the
hub bolt and for each material of the hub bolt and of the
wheel.
[0035] First, operating the setting buttons in setting portion 12A,
a proper axial force (rating value) of a hub bolt subject to
measurement is set, for example, at a predetermined range (a single
value is also available), and the size of the hub bolt, materials
and others are set (step S1 in FIG. 6). For example, it is assumed
that M20 is set as the bolt size, and that the material of the hub
bolt and the material (aluminum or steel) of the wheel to be
fastened by the hub bolt are set as the materials. By this means,
the comparison computing determination circuit 24 performs
comparison and determination using the correlation data between the
tap sound frequency and the axial bolt force corresponding to set
parameters. Further, as a proper axial force, for example, a range
of 7,500 kgf to 15,000 kgf (or a single value of 9,800 kfg that is
a standard axial force) is set.
[0036] Then, in a no-load state where any load is not mounted on
the vehicle (because the correlation data of the no-load state is
stored in comparison computing determination circuit 24 herein),
the impact chip 6A on the front end surface of the axial bolt force
measuring instrument 1A is brought into contact with the end
surface of the hub bolt (step S2 . . . the state in FIG. 1).
[0037] When the impact chip 6A comes into contact with the end
surface of the bolt, the trigger lever 2A is depressed to operate
(step S3). In this way, a trigger signal is input to the driving
control portion 22 from the trigger lever 2A side, and in response
to the signal, the driving control portion 22 outputs a control
signal to drive the plunger solenoid 32 to the plunger solenoid 32.
As a result, the traveling driving portion of the plunger solenoid
32 travels back and forth in a stroke of about 5 mm, and
continuously hits the end surface of the hub bolt (step S4).
Herein, for example, the portion hits for about two seconds at
speed of about 3 taps/second.
[0038] The tap sound generated by hitting is collected by the sound
collecting microphone 8A (step S5), while being amplified by the
amplifier 26. Then, the sound signal as an amplified analog signal
is transformed into a frequency (step S6), and output to the
comparison computing determination circuit 24 as a digital
signal.
[0039] When the frequency data of the tap sound collected by the
sound collecting microphone 8A is thus input to the comparison
computing determination circuit 24, comparison computing
determination circuit 24 converts the input frequency data into an
axial bolt force (step S7) using the correlation data of tap sound
frequency/axial bolt force corresponding to the size of the hub
bolt and materials of the hub bolt and the wheel set in the setting
portion 12A, and determines whether or not the converted value
agrees with the set value set and input in the setting portion 12A
(whether or not the converted value is in a range of proper values
set and input in the setting portion 12A, when a predetermined
range is set and input as the proper axial force) by comparing the
values (step S8). Then, when determining that the converted value
agrees with the set value (or is in the set range), the comparison
computing determination circuit 24 displays the converted value
(measured axial bolt force) on the display of the display potion
10A, while lighting the LED, for example, displaying "OK" of the
display portion 10A (step S9). Further, at the same time, the
comparison computing determination circuit 24 outputs a signal
indicating that the measured axial bolt force is proper to the
driving control portion 22. By this means, the plunger solenoid
valve 30 is driven by the driving control portion 22, the ink is
sprayed to the bolt from the ink tank 36 via the inkjet nozzle 34,
and the bolt is thus provided with marking indicating such a result
of determination that the axial bolt force is proper (step
S10).
[0040] Meanwhile, when determining that the converted value does
not agree with the set value (or is not in the set range), the
comparison computing determination circuit 24 displays the
converted value (measured axial bolt force) on the display of the
display potion 10A, while lighting the LED, for example, displaying
"NG" of the display portion 10A (step S11). At this point, for
example, the LED displaying "HI" or "LOW" may be lighted, in order
to specifically display whether the converted value exceeds or
falls below the set value.
[0041] As described above, the axial bolt force measuring
instrument according to the present invention uses that the
correlation exists between the tap sound frequency of a bolt and
the axial force of the bolt, and is provided with the tapping
portion (6 and 6A) that taps the bolt, the sound collecting portion
(8 and 8A) that collects tap sound generated by tapping the bolt
with the tapping portion (6 and 6A), the frequency measuring
portion (28) that measures the frequency of the tap sound collected
by the sound collecting portion (28), and the axial force
converting portion (24) that converts the frequency of the tap
sound measured by the frequency measuring portion (28) into an
axial force of the bolt. Accordingly, without having the skill,
intuition and/or specific knowledge and experiment, it is possible
to accurately measure the axial bolt force (fastening state
subsequent to fastening of the bolt) with ease in a short time, and
targets for measurement are not limited particularly (excellent in
general versatility) because of not depending on the muscular
strength of a person.
[0042] Further, the axial bolt force measuring instrument according
to one embodiment of the present invention is provided with the
setting portion (12 and 12A) to set a predetermine axial bolt
force, and the comparing portion (24) that compares the set axial
force set in the setting portion (12 and 12A) with a converted
axial force converted in the axial force converting portion (24)
from the tap sound frequency. Therefore, it is possible to
accurately recognize whether or not the bolt subject to measurement
has a predetermined axial force (whether the bolt is tightened by a
predetermined tightening force), i.e. lack of tightening,
forgetting to tighten or excess tightening of the bolt.
[0043] Furthermore, in the axial bolt force measuring instrument
according to one embodiment of the present invention, the axial
force converting portion (24) converts the tap sound frequency into
an axial bolt force corresponding to various parameters such as the
size of the bolt and materials of the bolt and member to fasten by
the bolt. Therefore, it is possible to perform accurate
frequency-axial force conversion, and thus the accuracy is improved
in measuring the axial bolt force.
[0044] Still furthermore, the axial bolt force measuring instrument
according to one embodiment of the present invention is formed of
the measuring instrument body (42) internally provided with the
tapping portion (6 and 6A), sound collecting portion (8 and 8A),
frequency measuring portion (28), and axial force converting
portion (24), and of the handle portion (40) which enables grasp
thereof by hand, extends from the measuring instrument body (42)
and has the initiation portion (2 and 2A) to initiate the tapping
portion (6 and 6A), and has the internal battery (20) that supplies
power required for measurement of the axial bolt force. It is thus
possible to use the instrument at any places readily (with
excellence in portability) without restrictions in indoor and
outdoor weather conditions and power supply.
[0045] In addition, as a matter of course, the present invention is
not limited to the aforementioned embodiment, and is capable of
being carried into practice with various modifications thereof
without departing from the subject matter of the present invention.
For example, the display portion 10A displays a measured value as
an axial bolt force (kgf) in the aforementioned embodiment, but may
display a tightening torque (T), tension (N), or tap sound
frequency (Hz) as a measured value. Further, the setting portion
12A enables setting and input of a predetermined axial bolt force,
but may enable setting and input of a tap sound frequency
corresponding to the predetermined axial bolt force. In this case,
without using the correlation data to convert the tap sound
frequency into the axial bolt force, it is possible to directly
compare a measured frequency with the set frequency in the
comparison computing determination circuit 24. This scheme is
effective in the case where the tap sound frequency is beforehand
obtained corresponding to the proper axial force. Further, in this
case, by causing the display portion 10A to display a measured tap
sound frequency, instead of a measured axial force, the measuring
instrument becomes a bolt tap sound frequency measuring instrument,
rather than the axial bolt force measuring instrument. Furthermore,
in the aforementioned embodiment, the setting portion 12A is
provided so as to response to axial force measurements with various
bolt sizes and materials, and corresponding to parameters set and
input in the setting portion 12A, the correlation data is selected
and an axial force is measured from the tap sound frequency.
However, in the case where the axial bolt force measuring
instrument is used only for bolts with a predetermined size and
material, since the common correlation data is used, the need is
eliminated of providing the setting portion on purpose.
* * * * *